1. Field of the Invention
This invention relates to new and useful improvements in shock subs positioned in the drilling string above the drilling bit to absorb vibrations, shock or impact loading otherwise imparted to the drilling string from the drilling bit during the drilling of wells for the production of crude oil, natural gas, geothermal energy, etc.
2. Brief Description of the Prior Art
Large axial displacement drill string vibrations occur in hard formations when drilling against a non-flat surface, a non-homogeneous (hard-soft) surface or a highly fractured surface. When the drilling is carried out using a conventional tricone bit, the vibration or shock or impact loading is multiplied by a factor of three in frequency and substantial impact and vibratory forces are applied in the drill string which results in early failure of tool joints, drill collars, and other portions of the drill string.
Shock absorbers in the form of shock subs which are generally run immediately above the drill bit in a drill string were first developed more than 40 years ago and have been improved in a variety of features over the years since their original introduction. Crowell U.S. Pat. No. 1,767,350 and Archer U.S. Pat. No. 1,960,688 disclose two of the earliest forms of drill string shock absorbers which utilized an elastomeric sleeve to dampen both axial and torsional vibrations. Other U.S. Patents which disclose significant improvements on shock absorbers utilizing elastomeric springs include the following: Gill et al 2,025,100, Crickmer 2,620,165, Ortloff 2,740,651, Vertson 2,765,147, Regland 2,795,398, 3,033,011, Garrett 3,099,918, Crane 3,156,106, Hughes 3,257,827, Wiggins 3,274,798, Coulter 3,301,009, Hughes 3,306,078, Vertson 3,323,326, Leather et al 3,323,327, Haushalter 2,325,132, Davidescu 3,503,224, Zerb et al 3,660,990, Mason 3,949,150.
Another type of rotary shock absorber or shock sub utilizes a compressible fluid as the shock absorbing medium. U.S. Pat. Nos. illustrating this type of shock absorber include the following: Leathers 3,225,566, Frocks 3,230,740, Harrison 3,350,900, Galle 3,382,936, Galle 3,746,329, Webb 3,998,443.
Still another type of shock absorber utilizes a helical spring as the shock absorbing member, U.S. Pat. Nos. which illustrate this type of shock absorber include the following: Ponti 1,785,559, Reed 2,240,519, Allen 2,712,437, Warren 2,991,635, Blair 3,122,902, Karle 3,963,228.
Still another form of shock absorber utilizes a torsional spring as the shock absorbing member. U.S. Pat. Nos. illustrating this principle include the following: Mullins 3,947,008, Amtsperg 3,939,670, Frocks 3,339,380. Manion 2,570,577 discloses the use of annular disc type plate springs as shock absorbing elements. Salvatori et al 3,383,126 and Falkner 3,406,537 disclose the use of wire mesh springs as the shock absorbing member. Garrett 3,254,508 and Wiggins 3,263,446 disclose the use of a bellows as a shock absorber. Bergstrom 4,211,440; Ostertag 4,194,582; and Aumann 4,186,569 disclose shock subs using various kinds of spring washers. Nixon 4,162,619 discloses a shock sub for absorbing rotary as well as longitudinal shocks. Ashfield et al 4,043,546 disclose certain novel compression spring washers.